Representing Energy Changes Graphically Abinethaa Paramasivam| February 12, 2015 The changes in energy for a chemical system can be represented graphically using a potential energy diagram. The reaction coordinate or reaction progress is the x-axis.These graphs plot potential energy vs. reaction progress. The potential energy is the y axis. Delta H is calculated by determining the difference in potential energy between the reactants and products.Endothermic Reactions
Exothermic Reactions activation energy- minimum amount of energy required by reactants for reaction to occurActivated complex= collision state Ea in exothermic reaction is lower than an endothermic reaction. How do you calculate Ea for reverse? Answer: products to activated complex.
Example: Calculate heat produced by combustion of 2.4gram of ethane.
C2H6 (g) + 7/2 O2(g) à 2CO2 (g)+ 3H2O (g) Mass= 2.4g
Molar Mass=30.08 g/mol N= 0.080mol Delta H= -1560kJ/mol
1mol/-1560kJ=0.080mol/x
x= (0.080mol) (-1560kJ/mol)
=-124.8kJ q=-124.8kJ Therefore the heat produced by combustion is -120kJ.
Homework Page 369 #17-18
Page 371 #12, 13, 15
Reminder: Quiz on Tuesday everything learned until Hess Law (this material is not on the Quiz)
- Above graph is endothermic because product potential energy>reactants potential energy
Potential Energy Diagrams and Reaction Rate - lower activation energy greater, greater the rate of reaction - in general, exothermic reactions tend to have greater rates than endothermic reactions - many exothermic reactions are self-sustaining (can keep themselves going)
- if there is an increase in temperature, potential energy does not change - take this heat and have a vertical translation up; delta H does not change and activation energy does not change
- if a catalyst is added, activation energy decreases - catalyst increases the rate by providing an alternate pathway mechanism with a lower activation energy
Maxwell-Boltzman Distributions
To determine the total number of particles, that react then look at the patent area, calculate area in there and the number of particles that will react. - to increase rate, increase the area (by increasing the temperature)
Temperature changes shape of the graph because by increasing the temperature, you will increase the average kinetic energy..
Maxwell-Boltzman Distribution and Reaction Rates - increase rate of reaction, fraction of particles with activation energy or greater must increase.
- increase red and purple (temperature is bigger) more particles with minimum energy - purple area=lower temp= lower area
Homework: Read pages 366-367 Page 372 #11-16 Page 379 #9-10 Reminder: Unit test on Friday February 27 Formal Lab report due for heat lab due on Thursday February 26
Abinethaa Paramasivam| February 12, 2015
The changes in energy for a chemical system can be represented graphically using a potential energy diagram. The reaction coordinate or reaction progress is the x-axis. These graphs plot potential energy vs. reaction progress. The potential energy is the y axis. Delta H is calculated by determining the difference in potential energy between the reactants and products.Endothermic Reactions
Exothermic Reactions
activation energy- minimum amount of energy required by reactants for reaction to occurActivated complex= collision state
Ea in exothermic reaction is lower than an endothermic reaction. How do you calculate Ea for reverse? Answer: products to activated complex.
Example: Calculate heat produced by combustion of 2.4gram of ethane.
C2H6 (g) + 7/2 O2(g) à 2CO2 (g)+ 3H2O (g)
Mass= 2.4g
Molar Mass=30.08 g/mol
N= 0.080mol
Delta H= -1560kJ/mol
1mol/-1560kJ=0.080mol/x
x= (0.080mol) (-1560kJ/mol)
=-124.8kJ
q=-124.8kJ
Therefore the heat produced by combustion is -120kJ.
Homework
Page 369 #17-18
Page 371 #12, 13, 15
Reminder: Quiz on Tuesday everything learned until Hess Law (this material is not on the Quiz)
Watch these videos to review for Tuesday's quiz:
https://www.youtube.com/watch?v=f_jCFXoRX4w&index=10&list=WL
https://www.youtube.com/watch?v=JuWtBR-rDQk
Potential Energy Diagrams
Abinethaa Paramasivam|February 20, 2015
- Above graph is endothermic because product potential energy>reactants potential energy
Potential Energy Diagrams and Reaction Rate
- lower activation energy greater, greater the rate of reaction
- in general, exothermic reactions tend to have greater rates than endothermic reactions
- many exothermic reactions are self-sustaining (can keep themselves going)
- if there is an increase in temperature, potential energy does not change
- take this heat and have a vertical translation up; delta H does not change and activation energy does not change
- if a catalyst is added, activation energy decreases
- catalyst increases the rate by providing an alternate pathway mechanism with a lower activation energy
Maxwell-Boltzman Distributions
To determine the total number of particles, that react then look at the patent area, calculate area in there and the number of particles that will react.
- to increase rate, increase the area (by increasing the temperature)
Temperature changes shape of the graph because by increasing the temperature, you will increase the average kinetic energy..
Maxwell-Boltzman Distribution and Reaction Rates
- increase rate of reaction, fraction of particles with activation energy or greater must increase.
- increase red and purple (temperature is bigger)
more particles with minimum energy
- purple area=lower temp= lower area
Homework: Read pages 366-367
Page 372 #11-16
Page 379 #9-10
Reminder: Unit test on Friday February 27
Formal Lab report due for heat lab due on Thursday February 26
If you need more help, watch these videos:
https://www.youtube.com/watch?v=mGt73Eg0hjE
https://www.youtube.com/watch?v=48sLH9P8QK0